Thermistor made of metal nitride material, method for producing same, and film type thermistor sensor

ABSTRACT

Provided are a metal nitride material for a thermistor, which has a high reliability and a high heat resistance and can be directly deposited on a film or the like without firing, a method for producing the same, and a film type thermistor sensor. The metal nitride material for a thermistor consists of a metal nitride represented by the general formula: (Ti 1-w Cr w ) x Al y N z  (where 0.0&lt;w&lt;1.0, 0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, and x+y+z=1), wherein the crystal structure thereof is a hexagonal wurtzite-type single phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of PCTInternational Application No. PCT/JP2013/082518 filed Nov. 27, 2013,which claims the benefit of Japanese Patent Application No. 2012-279148,filed Dec. 21, 2012, the entire contents of the aforementionedapplications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a metal nitride material for athermistor, which can be directly deposited on a film or the likewithout firing, a method for producing the same, and a film typethermistor sensor.

Description of the Related Art

There is a demand for a thermistor material used for a temperaturesensor or the like having a high B constant in order to obtain a highprecision and high sensitivity thermistor sensor. Conventionally, oxidesof transition metals such as Mn, Co, Fe, and the like are typically usedas such thermistor materials (see Patent Documents 1 and 2). Thesethermistor materials need firing at a temperature of 600° C. or higherin order to obtain a stable thermistor characteristic/property.

In addition to thermistor materials consisting of metal oxides asdescribed above, Patent Document 3 discloses a thermistor materialconsisting of a nitride represented by the general formula:M_(x)A_(y)N_(z) (where “M” represents at least one of Ta, Nb, Cr, Ti,and Zr, “A” represents at least one of Al, Si, and B, 0.1≦x≦0.8,0<y≦0.6, 0.1≦z≦0.8, and x+y+z=1). In Patent Document 3, only aTa—Al—N-based material consisting of a nitride represented by thegeneral formula: M_(x)A_(y)N_(z) (where 0.5≦x≦0.8, 0.1≦y≦0.5, 0.2≦z≦0.7,and x+y+z=1) is described in an Example. The Ta—Al—N-based material isproduced by sputtering in a nitrogen gas-containing atmosphere using amaterial containing the element(s) listed above as a target. Theresultant thin film is subject to a heat treatment at a temperature from350 to 600° C. as required.

Other than thermistor materials, Patent document 4 discloses aresistance film material for a strain sensor, which consists of anitride represented by the general formula: Cr_(100-x-y)N_(x)M_(y)(where “M” is one or more elements selected from Ti, V, Nb, Ta, Ni, Zr,Hf, Si, Ge, C, O, P, Se, Te, Zn, Cu, Bi, Fe, Mo, W, As, Sn, Sb, Pb, B,Ga, In, Tl, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, Be, Mg, Ca, Sr, Ba,Mn, Al, and rare earth elements, the crystal structure thereof iscomposed of mainly a bcc structure or mainly a mixed structure of a bccstructure and A15 type structure, 0.0001≦x≦30, 0≦y≦30, and0.0001≦x+y≦50). The resistance film material for a strain sensor isemployed for measuring strain and stress from changes in the resistanceof the sensor made of a Cr—N-based strain resistance film, where both ofthe amounts of nitrogen (x) and an accessory component element(s) M (y)are 30 at % or lower, as well as for performing various conversions. TheCr—N-M-based material is produced by reactive sputtering in a depositionatmosphere containing the accessory gaseous element(s) using a materialcontaining the above-described element(s) or the like as a target. Theresultant thin film is subject to a heat treatment at a temperature from200 to 1000° C. as required.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application    Publication No. 2003-226573-   [Patent Document 2] Japanese Unexamined Patent Application    Publication No. 2006-324520-   [Patent Document 3] Japanese Unexamined Patent Application    Publication No. 2004-319737-   [Patent Document 4] Japanese Unexamined Patent Application    Publication No. H10-270201

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The following problems still remain in the conventional techniquesdescribed above.

In recent years, the development of a film type thermistor sensor madeof a thermistor material formed on a resin film has been considered, andthus, it has been desired to develop a thermistor material that can bedirectly deposited on a film. Specifically, it is expected that aflexible thermistor sensor will be obtained by using a film.Furthermore, it is desired to develop a very thin thermistor sensorhaving a thickness of about 0.1 mm. However, a substrate material usinga ceramic material such as alumina that has often been conventionallyused has a problem that if the substrate material is thinned to athickness of 0.1 mm for example, the substrate material is very fragileand breaks easily. Thus, it is expected that a very thin thermistorsensor will be obtained by using a film.

However, a film made of a resin material typically has a low heatresistance temperature of 150° C. or lower, and even polyimide, which isknown as a material having a relatively high heat resistancetemperature, only has a heat resistance temperature of about 200° C.Hence, when a heat treatment is performed in a process of forming athermistor material, it has been conventionally difficult to use such athermistor material. The above-described conventional oxide thermistormaterial needs to be fired at a temperature of 600° C. or higher inorder to realize a desired thermistor characteristic, so that a filmtype thermistor sensor that is directly deposited on a film cannot berealized. Thus, it has been desired to develop a thermistor materialthat can be directly deposited on a film without firing. However, eventhe thermistor material disclosed in Patent Document 3 still needs aheat treatment on the resultant thin film at a temperature from 350 to600° C. as required in order to obtain a desired thermistorcharacteristic. Regarding this thermistor material, a B constant ofabout 500 to 3000 K was obtained in an Example of the Ta—Al—N-basedmaterial, but the heat resistance of this material is not described andtherefore, the thermal reliability of a nitride-based material isunknown.

In addition, the Cr—N-M-based material disclosed in Patent document 4has a low B constant of 500 or lower and cannot ensure heat resistanceto a temperature of 200° C. or lower unless a heat treatment in therange of 200° C. to 1000° C. is performed, and thus, a film typethermistor sensor that is directly deposited on a film cannot berealized. Therefore, it has been desired to develop a thermistormaterial that can be directly deposited on a film without firing.

The present invention has been made in view of the aforementionedcircumstances, and an object of the present invention is to provide ametal nitride material for a thermistor, which has a high reliabilityand a high heat resistance and can be directly deposited on a film orthe like without firing, a method for producing the same, and a filmtype thermistor sensor.

Means for Solving the Problems

The present inventors' serious endeavor carried out by focusing on anAl—N-based material among nitride materials found that the Al—N-basedmaterial having a good B constant and an excellent heat resistance maybe obtained without firing by substituting the Al site with a specificmetal element for improving electric conductivity and by forming it intoa specific crystal structure even though Al—N is an insulator anddifficult to provide with an optimum thermistor characteristic (Bconstant: about 1000 to 6000 K).

Therefore, the present invention has been made on the basis of the abovefinding, and adopts the following configuration in order to overcome theaforementioned problems.

Specifically, a metal nitride material for a thermistor according to afirst aspect of the present invention is characterized by a metalnitride material used for a thermistor, which consists of a metalnitride represented by the general formula:(Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z) (where 0.0<w<1.0, 0.70≦y/(x+y)≦0.95,0.4≦z≦0.5, and x+y+z=1), wherein the crystal structure thereof is ahexagonal wurtzite-type single phase.

Since this metal nitride material for a thermistor consists of a metalnitride represented by the general formula:(Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z) (where 0.0<w<1.0, 0.70≦y/(x+y)≦0.95,0.4≦z≦0.5, and x+y+z=1), wherein the crystal structure thereof is ahexagonal wurtzite-type single phase, a good B constant and an high heatresistance can be obtained without firing.

Note that, when the value of “y/(x+y)” (i.e., Al/(Ti+Cr+Al)) is lessthan 0.70, a wurtzite-type single phase cannot be obtained, but twocoexisting phases of a wurtzite-type phase and a NaCl-type phase or asingle phase of only a NaCl-type phase may be obtained, so that asufficiently high resistance and a high B constant cannot be obtained.

When the value of “y/(x+y)” (i.e., Al/(Ti+Cr+Al)) exceeds 0.95, themetal nitride material exhibits very high resistivity and extremely highelectrical insulation, so that the metal nitride material is notapplicable as a thermistor material.

When the value of “z” (i.e., N/(Ti+Cr+Al+N)) is less than 0.4, thenitridation amount of metals is too small to obtain a wurtzite-typesingle phase. Consequently, a sufficiently high resistance and a high Bconstant cannot be obtained.

In addition, when the value of “z” (i.e., N/(Ti+Cr+Al+N)) exceeds 0.5, awurtzite-type single phase cannot be obtained. This is because thestoichiometric ratio of N/(Ti+Cr+Al+N) in a wurtzite-type single phasein the absence of defects at the nitrogen site is 0.5.

Regarding the value of “w” (i.e., Cr/(Ti+Cr)), if the condition of0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, and x+y+z=1 is satisfied, a wurtzite-typesingle phase can be obtained in a wide composition range of 0.0<w<1.0,thus a sufficiently high resistance and a high B constant can beobtained.

A metal nitride material for a thermistor according to a second aspectof the present invention is characterized in that the metal nitridematerial for a thermistor according to the first aspect of the presentinvention is deposited as a film, and is a columnar crystal extending ina vertical direction with respect to the surface of the film.

Specifically, since this metal nitride material for a thermistor is acolumnar crystal extending in a vertical direction with respect to thesurface of the film, the crystallinity of the film is high, so that ahigh heat resistance can be obtained.

A metal nitride material for a thermistor according to a third aspect ofthe present invention is characterized in that the metal nitridematerial according to the first or second aspect of the presentinvention is deposited as a film and is more strongly oriented along ac-axis than an a-axis in a vertical direction with respect to thesurface of the film.

Specifically, since this metal nitride material for a thermistor is morestrongly oriented along the c-axis than the a-axis in a verticaldirection with respect to the surface of the film, a high B constant ascompared with the case of the strong a-axis orientation and further anexcellent reliability in heat resistance can be obtained.

A film type thermistor sensor according to a fourth aspect of thepresent invention is characterized by including an insulating film; athin film thermistor portion made of the metal nitride material for athermistor according to any one of the first to third aspects of thepresent invention on the insulating film; and a pair of patternelectrodes formed at least on the top or the bottom of the thin filmthermistor portion.

Specifically, since the thin film thermistor portion made of the metalnitride material for a thermistor according to any one of the first tothird aspects of the present invention is formed on the insulating filmin this film type thermistor sensor, an insulating film having a lowheat resistance such as a resin film can be used because the thin filmthermistor portion is formed without firing and has a high B constantand a high heat resistance, so that a thin and flexible thermistorsensor having an excellent thermistor characteristic can be obtained.

A substrate material employing a ceramic such as alumina that has oftenbeen conventionally used has a problem that if the substrate material isthinned to a thickness of 0.1 mm for example, the substrate material isvery fragile and breaks easily. On the other hand, since a film can beused in the present invention, a very thin film type thermistor sensorhaving a thickness of 0.1 mm, for example, can be obtained.

A film type thermistor sensor according to a fifth aspect of the presentinvention is characterized in that at least a portion of a pair of thepattern electrodes that is bonded to the thin film thermistor portion ismade of Cr in the film type thermistor sensor according to a fourthaspect of the present invention.

Specifically, since at least a portion of a pair of the patternelectrodes that is bonded to the thin film thermistor portion is made ofCr in this film type thermistor sensor, the bondability between the thinfilm thermistor portion made of Ti—Cr—Al—N and a portion made of Cr of apair of the pattern electrodes becomes high. In other words, since Crthat is one of the elements constituting the thin film thermistorportion is used as the material for the bonding portion of a pair of thepattern electrodes, the bondability between both the portions becomeshigh, and thus a high reliability can be obtained.

A method for producing a metal nitride material for a thermistoraccording to a sixth aspect of the present invention is characterized inthat the method for producing the metal nitride material for athermistor according to any one of the first to third aspects of thepresent invention includes a deposition step of performing filmdeposition by reactive sputtering in a nitrogen-containing atmosphereusing a Ti—Cr—Al composite sputtering target.

Specifically, since film deposition is performed by reactive sputteringin a nitrogen-containing atmosphere using a Ti—Cr—Al compositesputtering target in this method for producing a metal nitride materialfor a thermistor, the metal nitride material for a thermistor of thepresent invention, which consists of the (Ti,Cr)AlN described above, canbe deposited on a film without firing.

A method for producing a metal nitride material for a thermistoraccording to a seventh aspect of the present invention is characterizedby the method according to a sixth aspect of the present invention,wherein the sputtering gas pressure during the reactive sputtering isset to less than 0.67 Pa.

Specifically, since the sputtering gas pressure during the reactivesputtering is set to less than 0.67 Pa in this method for producing ametal nitride material for a thermistor, a film made of the metalnitride material for a thermistor according to a third aspect of thepresent invention can be formed which is more strongly oriented alongthe c-axis than the a-axis in a vertical direction with respect to thesurface of the film.

A method for producing a metal nitride material for a thermistoraccording to an eighth aspect of the present invention is characterizedin that the method according to a sixth or seventh aspect of the presentinvention includes a step of irradiating the formed film with nitrogenplasma after the deposition step.

Specifically, since the formed film is irradiated with nitrogen plasmaafter the deposition step in this method for producing a metal nitridematerial for a thermistor, nitrogen defects in the film are reduced,resulting in a further improvement in heat resistance.

Effects of the Invention

According to the present invention, the following effects may beprovided.

Specifically, since the metal nitride material for a thermistoraccording to the present invention consists of a metal nitriderepresented by the general formula: (Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z)(where 0.0<w<1.0, 0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, and x+y+z=1), whereinthe crystal structure thereof is a hexagonal wurtzite-type single phase,the metal nitride material having a good B constant and an high heatresistance can be obtained without firing. Also, since film depositionis performed by reactive sputtering in a nitrogen-containing atmosphereusing a Ti—Cr—Al composite sputtering target in the method for producingthe metal nitride material for a thermistor according to the presentinvention, the metal nitride material for a thermistor of the presentinvention, which consists of the (Ti,Cr)AlN described above, can bedeposited on a film without firing. Further, since a thin filmthermistor portion made of the metal nitride material for a thermistoraccording to the present invention is formed on an insulating film inthe film type thermistor sensor according to the present invention, athin and flexible thermistor sensor having an excellent thermistorcharacteristic can be obtained by using an insulating film such as aresin film having a low heat resistance. Furthermore, since a substratematerial is a resin film rather than a ceramic material that becomesvery fragile and breaks easily when being thinned, a very thin film typethermistor sensor having a thickness of 0.1 mm can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a (Ti+Cr)—Al—N-based ternary phase diagram illustrating thecomposition range of a metal nitride material for a thermistor accordingto one embodiment of a metal nitride material for a thermistor, a methodfor producing the same, and a film type thermistor sensor of the presentinvention.

FIG. 2 is a perspective view illustrating a film type thermistor sensoraccording to the present embodiment.

FIG. 3 is a perspective view illustrating a method for producing a filmtype thermistor sensor in the order of the steps according to thepresent embodiment.

FIG. 4 is a front view and a plan view illustrating a film evaluationelement for a metal nitride material for a thermistor according to anExample of a metal nitride material for a thermistor, a method forproducing the same, and a film type thermistor sensor of the presentinvention.

FIG. 5 is a graph illustrating the relationship between a resistivity at25° C. and a B constant according to Examples and a Comparative Exampleof the present invention.

FIG. 6 is a graph illustrating the relationship between a Al/(Ti+Cr+Al)ratio and a B constant according to Examples and a Comparative Exampleof the present invention.

FIG. 7 is a graph illustrating the relationship between a Cr/(Ti+Cr)ratio and a B constant according to Examples and a Comparative Exampleof the present invention.

FIG. 8 is a graph illustrating the result of X-ray diffraction (XRD) inthe case of a strong c-axis orientation, where Al/(Ti+Cr+Al)=0.76according to an Example of the present invention.

FIG. 9 is a graph illustrating the result of X-ray diffraction (XRD) inthe case of a strong a-axis orientation, where Al/(Ti+Cr+Al)=0.76according to an Example of the present invention.

FIG. 10 is a graph illustrating the result of X-ray diffraction (XRD) inthe case where Al/(Ti+Cr+Al)=0.61 according to a Comparative Example ofthe present invention.

FIG. 11 is a graph illustrating the relationship between a Al/(Ti+Cr+Al)ratio and a B constant for the comparison of the material exhibiting astrong a-axis orientation and the material exhibiting a strong c-axisorientation according to Examples of the present invention.

FIG. 12 is a graph illustrating the relationship between a Cr/(Ti+Cr)ratio and a B constant for the comparison of the material exhibiting astrong a-axis orientation and the material exhibiting a strong c-axisorientation according to Examples of the present invention.

FIG. 13 is a cross-sectional SEM photograph illustrating the materialexhibiting a strong c-axis orientation according to an Example of thepresent invention.

FIG. 14 is a cross-sectional SEM photograph illustrating the materialexhibiting a strong a-axis orientation according to an Example of thepresent invention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a description will be given of a metal nitride material fora thermistor, a method for producing the same, and a film typethermistor sensor according to one embodiment of the present inventionwith reference to FIGS. 1 to 3. In the drawings used in the followingdescription, the scale of each component is changed as appropriate sothat each component is recognizable or is readily recognized.

The metal nitride material for a thermistor of the present embodiment isa metal nitride material used for a thermistor, which consists of ametal nitride represented by the general formula:(Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z) (where 0.0<w<1.0, 0.70≦y/(x+y)≦0.95,0.4≦z≦0.5, and x+y+z=1), wherein the crystal structure thereof is ahexagonal wurtzite-type (space group: P6₃mc (No. 186)) single phase.Specifically, this metal nitride material for a thermistor consists of ametal nitride having a composition within the region enclosed by thepoints A, B, C, and D in the (Ti+Cr)—Al—N-based ternary phase diagram asshown in FIG. 1, wherein the crystal phase thereof is wurtzite-type.

Note that the composition ratios of (x, y, z) at the points A, B, C, andD are A (15, 35, 50), B (2.5, 47.5, 50), C (3, 57, 40), and D (18, 42,40), respectively.

Also, this metal nitride material for a thermistor is deposited as afilm, and is a columnar crystal extending in a vertical direction withrespect to the surface of the film. Furthermore, it is preferable thatthe metal nitride material for a thermistor is more strongly orientedalong the c-axis than the a-axis in a vertical direction with respect tothe surface of the film.

Note that the decision about whether a metal nitride material for athermistor has a strong a-axis orientation (100) or a strong c-axisorientation (002) in a vertical direction (film thickness direction)with respect to the surface of the film is made by examining theorientation of the crystal axis using X-ray diffraction (XRD). When thepeak intensity ratio of “the peak intensity of (100)”/“the peakintensity of (002)”, where (100) is the hkl index indicating a-axisorientation and (002) is the hkl index indicating c-axis orientation, isless than 1, the metal nitride material for a thermistor is determinedto have a strong c-axis orientation.

Next, a description will be given of a film type thermistor sensor usingthe metal nitride material for a thermistor of the present embodiment.As shown in FIG. 2, a film type thermistor sensor 1 includes aninsulating film 2, a thin film thermistor portion 3 made of the metalnitride material for a thermistor described above on the insulating film2, and a pair of pattern electrodes 4 formed at least on the thin filmthermistor portion 3.

The insulating film 2 is, for example, a polyimide resin sheet formed ina band shape. The insulating film 2 may be made of another material suchas polyethylene terephthalate (PET), polyethylene naphthalate (PEN), orthe like.

A pair of the pattern electrodes 4 has a pair of comb shaped electrodeportions 4 a that is patterned so as to have a comb shaped pattern byusing stacked metal films of, for example, a Cr film and an Au film, andis arranged opposite to each other, and a pair of linear extendingportions 4 b extending with the tip ends thereof being connected tothese comb shaped electrode portions 4 a and the base ends thereof beingarranged at the end of the insulating film 2.

A plating portion 4 c such as Au plating is formed as a lead wiredrawing portion on the base end of each of a pair of the linearextending portions 4 b. One end of the lead wire is joined with theplating portion 4 c via a solder material or the like. Furthermore,except for the end of the insulating film 2 including the platingportions 4 c, a polyimide coverlay film 5 is pressure bonded onto theinsulating film 2. Instead of the polyimide coverlay film 5, a polyimideor epoxy-based resin material may be formed onto the insulating film 2by printing.

A description will be given below of a method for producing the metalnitride material for a thermistor and a method for producing the filmtype thermistor sensor 1 using the metal nitride material for athermistor with reference to FIG. 3.

Firstly, the method for producing the metal nitride material for athermistor according to the present embodiment includes a depositionstep of performing film deposition by reactive sputtering in anitrogen-containing atmosphere using a Ti—Cr—Al composite sputteringtarget. The Ti—Cr—Al composite sputtering target is a Ti—Cr—Al sinteredbody that is prepared by mixing a Ti—Al alloy powder and a Cr—Al alloypowder together and then compacting them by hot pressing.

It is preferable that the sputtering gas pressure during the reactivesputtering is set to less than 0.67 Pa.

Furthermore, it is preferable that the formed film is irradiated withnitrogen plasma after the deposition step.

More specifically, the thin film thermistor portion 3 having a thicknessof 200 nm, which is made of the metal nitride material for a thermistorof the present embodiment, is deposited on the insulating film 2 whichis, for example, a polyimide film having a thickness of 50 μm shown inFIG. 3(a) by the reactive sputtering method, as shown in FIG. 3(b). Theexemplary sputtering conditions at this time are as follows: an ultimatedegree of vacuum: 5×10⁻⁶ Pa, a sputtering gas pressure: 0.4 Pa, a targetinput power (output): 200 W, and a nitrogen gas partial pressure under amixed gas (Ar gas+nitrogen gas) atmosphere: 60%. In addition, the metalnitride material for a thermistor having a desired size is deposited onthe insulating film 2 using a metal mask so as to form the thin filmthermistor portion 3. It is preferable that the formed thin filmthermistor portion 3 is irradiated with nitrogen plasma. For example,the thin film thermistor portion 3 is irradiated with nitrogen plasmaunder the degree of vacuum of 6.7 Pa, the output of 200 W, and the N₂gas atmosphere.

Next, a Cr film having a thickness of 20 nm is formed and an Au filmhaving a thickness of 200 nm is further formed thereon by the sputteringmethod, for example. Furthermore, a resist solution is coated on thestacked metal films using a barcoater, and then pre-baking is performedfor 1.5 minutes at a temperature of 110° C. After the exposure by anexposure device, any unnecessary portion is removed by a developingsolution, and then patterning is performed by post-baking for 5 minutesat a temperature of 150° C. Then, any unnecessary electrode portion issubject to wet etching using commercially available Au etchant and Cretchant, and then the resist is stripped so as to form a pair of thepattern electrodes 4 each having a desired comb shaped electrode portion4 a as shown in FIG. 3(c). Note that a pair of the pattern electrodes 4may be formed in advance on the insulating film 2, and then the thinfilm thermistor portion 3 may be deposited on the comb shaped electrodeportions 4 a. In this case, the comb shaped electrode portions 4 a of apair of the pattern electrodes 4 are formed below the thin filmthermistor portion 3.

Next, as shown in FIG. 3(d), the polyimide coverlay film 5 with anadhesive having a thickness of 50 μm, for example, is placed on theinsulating film 2, and then they are bonded to each other underpressurization of 2 MPa at a temperature of 150° C. for 10 minutes usinga press machine. Furthermore, as shown in FIG. 3(e), an Au thin filmhaving a thickness of 2 μm is formed at the base ends of the linearextending portions 4 b using, for example, an Au plating solution so asto form the plating portions 4 c.

When a plurality of film type thermistor sensors 1 is simultaneouslyproduced, a plurality of thin film thermistor portions 3 and a pluralityof pattern electrodes 4 are formed on a large-format sheet of theinsulating film 2 as described above, and then, the resultinglarge-format sheet is cut into a plurality of segments so as to obtain aplurality of film type thermistor sensors 1.

In this manner, a thin film type thermistor sensor 1 having a size of25×3.6 mm and a thickness of 0.1 mm, for example, is obtained.

As described above, since the metal nitride material for a thermistor ofthe present embodiment consists of a metal nitride represented by thegeneral formula: (Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z) (where 0.0<w<1.0,0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, and x+y+z=1), wherein the crystalstructure thereof is a hexagonal wurtzite-type single phase, a good Bconstant and a high heat resistance can be obtained without firing.

Since the metal nitride material for a thermistor is a columnar crystalextending in a vertical direction with respect to the surface of thefilm, the crystallinity of the film is high, so that a high heatresistance can be obtained.

Furthermore, since the metal nitride material for a thermistor is morestrongly oriented along the c-axis than the a-axis in a verticaldirection with respect to the surface of the film, a high B constant ascompared with the case of a strong a-axis orientation can be obtained.

Since film deposition is performed by reactive sputtering in anitrogen-containing atmosphere using a Ti—Cr—Al composite sputteringtarget in the method for producing the metal nitride material for athermistor of the present embodiment, the metal nitride material for athermistor, which consists of the (Ti,Cr)AlN described above, can bedeposited on a film without firing.

In addition, when the sputtering gas pressure during the reactivesputtering is set to less than 0.67 Pa, a film of the metal nitridematerial for a thermistor, which is more strongly oriented along thec-axis than the a-axis in a vertical direction to the surface of thefilm, can be formed.

Furthermore, since the formed film is irradiated with nitrogen plasmaafter the deposition step, nitrogen defects in the film are reduced,resulting in a further improvement in heat resistance.

Thus, since the thin film thermistor portion 3 made of the metal nitridematerial for a thermistor described above is formed on the insulatingfilm 2 in the film type thermistor sensor 1 using the metal nitridematerial for a thermistor of the present embodiment, the insulating film2 having a low heat resistance, such as a resin film, can be usedbecause the thin film thermistor portion 3 is formed without firing andhas a high B constant and a high heat resistance, so that a thin andflexible thermistor sensor having an excellent thermistor characteristiccan be obtained.

A substrate material using a ceramic such as alumina that has often beenconventionally used has a problem that if the substrate material isthinned to a thickness of 0.1 mm, for example, the substrate material isvery fragile and breaks easily. On the other hand, since a film can beused in the present invention, a very thin film type thermistor sensorhaving a thickness of 0.1 mm, for example, can be provided.

In addition, since at least a portion of a pair of the patternelectrodes 4 that is bonded to the thin film thermistor portion 3 ismade of a Cr film, the bondability between the thin film thermistorportion 3 made of Ti—Cr—Al—N and the Cr film of a pair of the patternelectrodes 4 becomes high. Specifically, since Cr that is one of theelements constituting the thin film thermistor portion 3 is used as thematerial for the bonding portion of a pair of the pattern electrodes 4,the bondability between both the portions becomes high, and thus a highreliability can be obtained.

EXAMPLES

Next, the evaluation results of the materials according to Examplesproduced based on the above embodiment regarding the metal nitridematerial for a thermistor, the method for producing the same, and thefilm type thermistor sensor according to the present invention will bespecifically described with reference to FIGS. 4 to 14.

<Production of Film Evaluation Element>

The film evaluation elements 121 shown in FIG. 4 were produced accordingto Examples and Comparative Examples of the present invention asfollows.

Firstly, each of the thin film thermistor portions 3 having a thicknessof 500 nm which were made of the metal nitride materials for athermistor with the various composition ratios shown in Table 1 wasformed on an Si wafer with a thermal oxidation film as an Si substrate(S) by using a Ti—Cr—Al composite target with various composition ratiosby the reactive sputtering method. The thin film thermistor portions 3were formed under the sputtering conditions of an ultimate degree ofvacuum of 5×10⁻⁶ Pa, a sputtering gas pressure of from 0.1 to 1 Pa, atarget input power (output) of from 100 to 500 W, and a nitrogen gaspartial pressure under a mixed gas (Ar gas+nitrogen gas) atmosphere offrom 10 to 100%.

Next, a Cr film having a thickness of 20 nm was formed and an Au filmhaving a thickness of 200 nm was further formed on each of the thin filmthermistor portions 3 by the sputtering method. Furthermore, a resistsolution was coated on the stacked metal films using a spin coater, andthen pre-baking was performed for 1.5 minutes at a temperature of 110°C. After the exposure by an exposure device, any unnecessary portion wasremoved by a developing solution, and then patterning was performed bypost-baking for 5 minutes at a temperature of 150° C. Then, anyunnecessary electrode portion was subject to wet etching usingcommercially available Au etchant and Cr etchant, and then the resistwas stripped so as to form a pair of pattern electrodes 124, each havinga desired comb shaped electrode portion 124 a. Then, the resultantelements were diced into chip elements so as to obtain the filmevaluation elements 121 used for evaluating a B constant and for testingheat resistance.

Note that the film evaluation elements 121 according to ComparativeExamples, each having the composition ratio of (Ti,Cr)_(x)Al_(y)N_(z)outside the range of the present invention and a different crystalsystem, were similarly produced for comparative evaluation.

<Film Evaluation>

(1) Composition Analysis

Elemental analysis was performed on the thin film thermistor portions 3obtained by the reactive sputtering method by X-ray photoelectronspectroscopy (XPS). In the XPS, a quantitative analysis was performed ona sputtering surface at a depth of 20 nm from the outermost surface byAr sputtering. The results are shown in Table 1. In the followingtables, the composition ratios are expressed by “at %”. Some of thesamples were also subject to a quantitative analysis for a sputteringsurface at a depth of 100 nm from the outermost surface to confirm thatit had the same composition within the quantitative accuracy as one inthe sputtering surface at a depth of 20 nm.

In the X-ray photoelectron spectroscopy (XPS), a quantitative analysiswas performed under the conditions of an X-ray source of MgKα (350 W), apath energy of 58.5 eV, a measurement interval of 0.125 eV, aphoto-electron take-off angle with respect to a sample surface of 45deg, and an analysis area of about 800 μmφ. Note that the quantitativeaccuracy of N/(Ti+Cr+Al+N) and Al/(Ti+Cr+Al) was ±2% and ±1%,respectively.

(2) Specific Resistance Measurement

The specific resistance of each of the thin film thermistor portions 3obtained by the reactive sputtering method was measured by thefour-probe method at a temperature of 25° C. The results are shown inTable 1.

(3) Measurement of B Constant

The resistance values for each of the film evaluation elements 121 attemperatures of 25° C. and 50° C. were measured in a constanttemperature bath, and a B constant was calculated based on theresistance values at temperatures of 25° C. and 50° C. The results areshown in Table 1.

In the B constant calculating method of the present invention, a Bconstant is calculated by the following formula using the resistancevalues at temperatures of 25° C. and 50° C.

B constant (K)=ln(R25/R50)/(1/T25-1/T50)

R25 (Ω): resistance value at 25° C.

R50 (Ω): resistance value at 50° C.

T25 (K): 298.15 K, which is an absolute temperature of 25° C. expressedin Kelvin

T50 (K): 323.15 K, which is an absolute temperature of 50° C. expressedin Kelvin

As can be seen from these results, a thermistor characteristic having aresistivity of 20 Ωcm or higher and a B constant of 1500 K or higher isachieved in all of the Examples in which the composition ratios of(Ti,Cr)_(x)Al_(y)N_(z) fall within the region enclosed by the points A,B, C, and D in the ternary phase diagram shown in FIG. 1, i.e., theregion where “0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, x+y+z=1”.

A Graph illustrating the relationship between a resistivity at 25° C.and a B constant from the above results is shown in FIG. 5. A graphillustrating the relationship between a Al/(Ti+Cr+Al) ratio and a Bconstant is also shown in FIG. 6. From these graphs, the film evaluationelements 121, the composition ratios of which fall within the regionwhere Al/(Ti+Cr+Al) is from 0.7 to 0.95 and N/(Ti+Cr+Al+N) is from 0.4to 0.5 and each crystal system of which is a hexagonal wurtzite-typesingle phase, have a specific resistance value at a temperature of 25°C. of 100 Ωcm or higher and a B constant of 1500 K or higher, which isthe region realizing a high resistance and a high B constant. In datashown in FIG. 6, the reason why the B constant varies with respect tothe same Al/(Ti+Cr+Al) ratio is because the film evaluation elements 121have different amounts of nitrogen in their crystals or differentamounts of lattice defects such as nitrogen defects.

Further, a graph illustrating the relationship between a Cr/(Ti+Cr)ratio and a B constant is shown in FIG. 7.

As can be seen from the above measurement results, if the condition thatAl/(Ti+Cr+Al) is from 0.7 to 0.95 and N/(Ti+Cr+Al+N) is from 0.4 to 0.5is satisfied, a specific resistance value at a temperature of 25° C. of100 Ωcm or higher and a B constant of 1500 K or higher, which is theregion of a high resistance and a high B constant, can be realized in awide composition range of 0.0<Cr/(Ti+Cr)<1.0.

In the materials according to Comparative Examples 2 and 3 as shown inTable 1, the composition ratios fall within the region whereAl/(Ti+Cr+Al)<0.7, and the crystal systems are cubic NaCl-type. Thus, amaterial with the composition ratio that falls within the region whereAl/(Ti+Cr+Al)<0.7 has a specific resistance value at a temperature of25° C. of less than 100 Ωcm and a B constant of less than 1500 K, whichis the region of low resistance and low B constant.

In the material according to Comparative Example 1 shown in Table 1, thecomposition ratio falls within the region where N/(Ti+Cr+Al+N) is lessthan 40%, that is, the material is in a crystal state where nitridationof metals contained therein is insufficient. The material according toComparative Example 1 was neither NaCl-type nor wurtzite-type and hadvery poor crystallinity. In addition, it was found that the materialaccording to this Comparative Example exhibited near-metallic behaviorbecause both the B constant and the resistance value were very small.

(4) Thin Film X-Ray Diffraction (Identification of Crystal Phase)

The crystal phases of the thin film thermistor portions 3 obtained bythe reactive sputtering method were identified by Grazing IncidenceX-ray Diffraction. The thin film X-ray diffraction is a small angleX-ray diffraction experiment. The measurement was performed under theconditions of a Cu X-ray tube, the angle of incidence of 1 degree, and2θ of from 20 to 130 degrees. Some of the samples were measured underthe condition of the angle of incidence of 0 degree and 2θ of from 20 to100 degrees.

As a result of the measurement, a wurtzite-type phase (hexagonalcrystal, the same phase as that of AlN) was obtained in the region whereAl/(Ti+Cr+Al)≧0.7, whereas a NaCl-type phase (cubic crystal, the samephase as those of CrN and TiN) was obtained in the region whereAl/(Ti+Cr+Al)<0.65. Note that it is contemplated that a crystal phase inwhich a wurtzite-type phase and a NaCl-type phase coexist will beobtained in the region where 0.65<Al/(Ti+Cr+Al)<0.7.

Thus, in the (Ti,Cr)AlN-based material, the region of high resistanceand high B constant can be realized by the wurtzite-type phase whereAl/(Ti+Cr+Al)≧0.7. In the materials according to Examples of the presentinvention, no impurity phase was confirmed and the crystal structurethereof was a wurtzite-type single phase.

In the material according to Comparative Example 1 shown in Table 1, thecrystal phase thereof was neither wurtzite-type nor NaCl-type asdescribed above, and thus, could not be identified in the testing. Inthis Comparative Example, the peak width of XRD was very large, showingthat the material had very poor crystallinity. It is contemplated thatthe crystal phase thereof was metal phase with insufficient nitridationbecause it exhibited near-metallic behavior from the viewpoint ofelectric characteristics.

TABLE 1 CRYSTAL AXIS EXHIBITING STRONG DEGREE RESULT OF XRD PEAK OFORIENTATION ELECTRIC INTENSITY IN VERTICAL PROPERTIES RATIO OF DIRECTIONWITH COMPOSITION RATIO SPECIFIC (100)/(002) RESPECT TO Ti/ Cr/ Al/ N/RESIS- WHEN SUBSTRATE SUR- (Ti + (Ti + (Ti + (Ti + Al/ TANCE CRYSTALFACE WHEN SPUTTER- Cr + Cr + Cr + Cr + (Ti + Cr/ VALUE PHASE IS CRYSTALPHASE ING GAS Al + Al + Al + Al + Cr + Ti + B CON- AT CRYSTAL WURTZITEIS WURTZITE TYPE PRESSURE N) N) N) N) Al) Cr) STANT 25° C. SYSTEM TYPE(a-AXIS OR c-AXIS) (Pa) (%) (%) (%) (%) (%) (%) (K) (Ω cm) COMPAR-INSUFFI- 4 14 50 32 74 78 7 9.E−02 ATIVE EX- CIENT AMPLE 1 NITRIDA- TIONCOMPAR- NaCl TYPE 18 4 35 43 61 18 821 4.E+01 ATIVE EX- AMPLE 2 COMPAR-NaCl TYPE 5 18 34 43 60 79 1171 6.E+01 ATIVE EX- AMPLE 3 EXAMPLE 1WURTZITE 0.43 c-AXIS <0.67 3 0.3 48 49 94 10 4581 1.E+06 TYPE EXAMPLE 2WURTZITE 0.79 c-AXIS <0.67 0.3 3 48 49 94 91 4035 1.E+06 TYPE EXAMPLE 3WURTZITE 0.05 c-AXIS <0.67 4 3 44 49 86 49 3439 6.E+05 TYPE EXAMPLE 4WURTZITE 0.10 c-AXIS <0.67 4 4 46 46 85 50 3057 1.E+05 TYPE EXAMPLE 5WURTZITE 0.19 c-AXIS <0.67 10 2 39 49 76 17 2532 9.E+04 TYPE EXAMPLE 6WURTZITE 0.31 c-AXIS <0.67 11 2 38 49 75 17 2701 6.E+04 TYPE EXAMPLE 7WURTZITE 0.58 c-AXIS <0.67 12 2 37 49 73 15 2452 4.E+03 TYPE EXAMPLE 8WURTZITE 4.04 a-AXIS ≧0.67 13 3 42 42 72 19 1773 7.E+02 TYPE EXAMPLE 9WURTZITE 2.96 a-AXIS ≧0.67 10 2 39 49 76 36 2132 2.E+05 TYPE EXAMPLEWURTZITE 1.75 a-AXIS ≧0.67 2 12 38 48 73 86 2377 9.E+04 10 TYPE EXAMPLEWURTZITE 2.04 a-AXIS ≧0.67 4 0.4 54 42 93 10 3312 6.E+05 11 TYPE

Next, since all the materials according to the Examples of the presentinvention were wurtzite-type phase films having strong orientation,whether the films have a strong a-axis orientation or c-axis orientationof the crystal axis in a vertical direction (film thickness direction)with respect to the Si substrate (S) was examined by XRD. At this time,in order to examine the orientation of the crystal axis, the peakintensity ratio of (100)/(002) was measured, where (100) is the hklindex indicating a-axis orientation and (002) is the hkl indexindicating c-axis orientation.

As a result of the measurement, in the Examples in which film depositionwas performed at a sputtering gas pressure of less than 0.67 Pa, theintensity of (002) was much stronger than that of (100), that is, thefilms exhibited stronger c-axis orientation than a-axis orientation. Onthe other hand, in the Examples in which film deposition was performedat a sputtering gas pressure of 0.67 Pa or higher, the intensity of(100) was much stronger than that of (002), that is, the films exhibitedstronger a-axis orientation than c-axis orientation.

Note that it was confirmed that a wurtzite-type single phase was formedin the same manner even when the thin film thermistor portion 3 wasdeposited on a polyimide film under the same deposition condition. Itwas also confirmed that the crystal orientation did not change even whenthe thin film thermistor portion 3 was deposited on a polyimide filmunder the same deposition condition.

An Exemplary XRD profile of the material according to the Exampleexhibiting strong c-axis orientation is shown in FIG. 8. In thisExample, Al/(Ti+Cr+Al) was equal to 0.76 (wurtzite-type, hexagonalcrystal), and the measurement was performed at 1 degree angle ofincidence. As can be seen from the result, the intensity of (002) wasmuch stronger than that of (100) in this Example.

An Exemplary XRD profile of the material according to the Exampleexhibiting strong a-axis orientation is also shown in FIG. 9. In thisExample, Al/(Ti+Cr+A) was equal to 0.76 (wurtzite-type, hexagonalcrystal), and the measurement was performed at 1 degree angle ofincidence. As can be seen from the result, the intensity of (100) wasmuch stronger than that of (002) in this Example.

The asterisk (*) in the graphs shows the peak originating from thedevice or the Si substrate with a thermal oxidation film, and thus, itwas confirmed that the peak with the asterisk (*) in the graphs wasneither the peak originating from a sample itself nor the peakoriginating from an impurity phase. A symmetrical measurement wasperformed at a 0 degree angle of incidence, confirming that the peakindicated by (*) is lost in the symmetrical measurement, and thus, thatit was the peak originating from the device or the Si substrate with athermal oxidation film.

An exemplary XRD profile in the Comparative Example is shown in FIG. 10.In this Comparative Example, Al/(Ti+Cr+Al) was equal to 0.61 (NaCl type,cubic crystal), and the measurement was performed at 1 degree angle ofincidence. No peak which could be indexed as a wurtzite-type (spacegroup: P6₃mc (No. 186)) was detected, and thus, the film according tothis Comparative Example was confirmed as a NaCl-type single phase.

Next, the correlations between a crystal structure and its electricproperties were further compared with each other in detail regarding theExamples of the present invention in which the wurtzite-type materialswere employed.

As shown in Table 2 and FIG. 11, the crystal axis of some materials isstrongly oriented along a c-axis in a vertical direction with respect tothe surface of the substrate and that of other materials is stronglyoriented along an a-axis in a vertical direction with respect to thesurface of the substrate among the materials having nearly the sameAl/(Ti+Cr+Al) ratio.

When both groups were compared to each other, it was found that thematerials having a strong c-axis orientation had a higher B constant byabout 200 K than that of the materials having a strong a-axisorientation provided that they have the same Al/(Ti+Cr+Al) ratio. Whenfocus was placed on the amount of N (i.e., N/(Ti+Cr+Al+N)), it was foundthat the materials having a strong c-axis orientation had a slightlylarger amount of nitrogen than that of the materials having a stronga-axis orientation. Since the ideal stoichiometric ratio ofN/(Ti+Cr+Al+N) is 0.5, it was found that the materials having a strongc-axis orientation were ideal materials due to a small amount ofnitrogen defects.

In addition, since three kinds of elements, Ti, Cr, and Al, are added tothe site of the metal element in a wurtzite-type material, these threekinds of metal elements, Ti, Cr, and Al, can eliminate the latticedistortion due to nitrogen defects, and thus a flexible nitridethermistor material having a higher reliability (heat resistance) can beprovided.

A graph illustrating the relationship between a Cr/(Ti+Cr) ratio and a Bconstant for the comparison of the material exhibiting a strong a-axisorientation and the material exhibiting a strong c-axis orientationaccording to Examples of the present invention is shown in FIG. 12. Inaddition, the data on the materials having nearly the same Al/(Ti+Cr+Al)ratio as that of the materials shown in FIG. 11 are plotted in FIG. 12.It has been found that the materials exhibiting a strong c-axisorientation have a higher B constant by about 200 K than the materialsexhibiting a strong a-axis orientation provided that they have the sameAl/(Ti+Cr+Al) and Cr/(Ti+Cr) ratios.

TABLE 2 CRYSTAL AXIS EXHIBITING STRONG DEGREE RESULT OF XRD PEAK OFORIENTATION ELECTRIC INTENSITY IN VERTICAL PROPERTIES RATIO OF DIRECTIONWITH COMPOSITION RATIO SPECIFIC (100)/(002) RESPECT TO Ti/ Cr/ Al/ N/RESIS- WHEN SUBSTRATE SUR- (Ti + (Ti + (Ti + (Ti + Al/ TANCE CRYSTALFACE WHEN SPUTTER- Cr + Cr + Cr + Cr + (Ti + Cr/ VALUE PHASE IS CRYSTALPHASE ING GAS Al + Al + Al + Al + Cr + Ti + B CON- AT CRYSTAL WURTZITEIS WURTZITE TYPE PRESSURE N) N) N) N) Al) Cr) STANT 25° C. SYSTEM TYPE(a-AXIS OR c-AXIS) (Pa) (%) (%) (%) (%) (%) (%) (K) (Ω cm) EXAMPLE 5WURTZITE 0.19 c-AXIS <0.67 10 2 39 49 76 17 2532 9.E+04 TYPE EXAMPLE 6WURTZITE 0.31 c-AXIS <0.67 11 2 38 49 75 17 2701 6.E+04 TYPE EXAMPLE 7WURTZITE 0.58 c-AXIS <0.67 12 2 37 49 73 15 2452 4.E+03 TYPE EXAMPLE 8WURTZITE 4.04 a-AXIS ≧0.67 13 3 42 42 72 19 1773 7.E+02 TYPE EXAMPLE 9WURTZITE 2.96 a-AXIS ≧0.67 10 2 39 49 76 16 2132 2.E+05 TYPE EXAMPLEWURTZITE 1.75 a-AXIS ≧0.67 2 12 38 48 73 86 2377 9.E+04 10 TYPE<Crystalline Form Evaluation>

Next, as an exemplary crystal form in the cross-section of the thin filmthermistor portion 3, a cross-sectional SEM photograph of the thin filmthermistor portion 3 according to the Example (where Al/(Ti+Cr+Al)=0.76,wurtzite-type, hexagonal crystal, and strong c-axis orientation), inwhich the thin film thermistor portion 3 having a thickness of about 250nm was deposited on the Si substrate (S) with a thermal oxidation film,is shown in FIG. 13. In addition, a cross-sectional SEM photograph ofthe thin film thermistor portion 3 according to another Example (whereAl/(Ti+Cr+Al)=0.76, wurtzite-type, hexagonal crystal, and strong a-axisorientation) is shown in FIG. 14.

The samples in these Examples were obtained by breaking the Sisubstrates (S) by cleavage. The photographs were taken by tiltobservation at an angle of 45 degrees.

As can be seen from these photographs, the samples were formed of ahigh-density columnar crystal in both Examples. Specifically, the growthof columnar crystals in a vertical direction with respect to the surfaceof the substrate was observed both in the Example revealing a strongc-axis orientation and in the Example revealing a strong a-axisorientation. Note that the break of the columnar crystal was generatedupon breaking the Si substrate (S) by cleavage. It was also confirmedthat when each film having a thickness of 200 nm, 500 nm, or 1000 nm wasdeposited on a Si substrate (S) with a thermal oxidation film, ahigh-density columnar crystal was similarly formed as described above.

<Heat Resistance Test Evaluation>

For the thin film thermistor portion 3 according to the Examples and theComparative Example shown in Table 3, a resistance value and a Bconstant before and after the heat resistance test at a temperature of125° C. for 1000 hours in air were evaluated. The results are shown inTable 3. The thin film thermistor portion 3 according to the ComparativeExample made of a conventional Ta—Al—N-based material was also evaluatedin the same manner for comparison.

As can be seen from these results, although the Al concentration and thenitrogen concentration vary, the heat resistance of the Ti—Cr—Al—N-basedmaterial based on the electric characteristic change before and afterthe heat resistance test is more excellent than that of theTa—Al—N-based material according to the Comparative Example when thecomparison is made by using the same B constant. Note that the materialsaccording to Examples 4 and 5 have a strong c-axis orientation, and thematerials according to Examples 9 and 10 have a strong a-axisorientation. When both groups are compared to each other, the heatresistance of the materials according to the Examples exhibiting astrong c-axis orientation is slightly improved as compared with that ofthe materials according to the Examples exhibiting a strong a-axisorientation.

Note that, in the Ta—Al—N-based material, the ionic radius of Ta is verylarge compared to that of Ti, Cr and Al, and thus, a wurtzite-type phasecannot be produced in the high-concentration Al region. It iscontemplated that the Ti—Cr—Al—N-based material having a wurtzite-typephase has a better heat resistance than the Ta—Al—N-based materialbecause the Ta—Al—N-based material is not a wurtzite-type phase.

TABLE 3 RISING RATE OF SPECIFIC RISING RATE SPECIFIC RESISTANCE OF BCONSTANT RESIS- AT 25° C. AFTER AFTER HEAT Al/ TANCE HEAT RESISTANCERESISTANCE M (M + B25- VALUE AT TEST AT 125° C. TEST AT 125° C. ELE- MAl N Al) 50 25° C. FOR 1,000 HOURS FOR 1,000 HOURS MENT (%) (%) (%) (%)(K) (Ω cm) (%) (%) COMPAR- Ta 60 1 39 2 2671 5.E+02 25 16 ATIVE EX-AMPLE EXAMPLE 4 (Ti, Cr) 8 46 46 85 3057 1.E+05 <4 <1 EXAMPLE 5 (Ti, Cr)12 39 49 76 2532 9.E+04 <4 <1 EXAMPLE 9 (Ti, Cr) 12 9 49 76 2132 2.E+05<5 <1 EXAMPLE (Ti, Cr) 14 38 48 73 2377 9.E+04 <5 <1 10<Heat Resistance Evaluation by Irradiation of Nitrogen Plasma>

After the thin film thermistor portion 3 according to Example 5 shown inTable 1 was deposited on the insulating film 2, the resulting film wasirradiated with nitrogen plasma under the degree of vacuum of 6.7 Pa,the output of 200 W, and the N₂ gas atmosphere. The results obtained bythe heat resistance tests of the film evaluation elements 121 with andwithout nitrogen plasma irradiation are shown in Table 4. As can be seenfrom the result, in the Example with nitrogen plasma irradiation, changein the specific resistance and the B constant is small, resulting in animprovement in heat resistance of the film. This is because thecrystallinity is improved by reduction in nitrogen defects in the filmby nitrogen plasma. It is more preferable that nitrogen plasma isradical nitrogen.

TABLE 4 RISING RATE OF SPECIFIC RESISTANCE AT 25° C. AFTER RISING RATEOF HEAT RESISTANCE B CONSTANT AFTER NITROGEN TEST AT 125° C. HEATRESISTANCE PLASMA FOR 1,000 HOURS TEST AT 125° C. FOR IRRADIATION (%)1,000 HOURS (%) YES <2 <1 NO (EXAMPLE 5) <4 <1

It can be seen from the above evaluation that a metal nitride materialmay exhibit an excellent thermistor characteristic when it is producedwithin a N/(Ti+Cr+Al+N) ratio of from 0.4 to 0.5. However, thestoichiometric ratio of N/(Ti+Cr+Al+N) is 0.5. Hence, it is found thatnitrogen defects are present in the material because the amount ofnitrogen is less than 0.5 in this test. Therefore, it is preferable toadd a process for compensating the nitrogen defects, and one preferredexample thereof is the nitrogen plasma irradiation described above.

The technical scope of the present invention is not limited to theaforementioned embodiments and Examples, but the present invention maybe modified in various ways without departing from the scope or teachingof the present invention.

REFERENCE NUMERALS

1: film type thermistor sensor, 2: insulating film, 3: thin filmthermistor portion, 4 and 124: pattern electrode

What is claimed is:
 1. A thermistor made of a metal nitride material,the metal nitride material consisting of a metal nitride represented bythe general formula: (Ti_(1-w)Cr_(w))_(x)Al_(y)N_(z) (where 0.0<w<1.0,0.70≦y/(x+y)≦0.95, 0.4≦z≦0.5, and x+y+z=1), wherein the crystalstructure thereof is a hexagonal wurtzite-type single phase.
 2. Thethermistor according to claim 1, wherein the metal nitride material isdeposited as a film and is a columnar crystal extending in a verticaldirection with respect to the surface of the film.
 3. The thermistoraccording to claim 1, wherein the metal nitride material is deposited asa film and is more strongly oriented along a c-axis than an a-axis in avertical direction with respect to the surface of the film.
 4. A filmtype thermistor sensor comprising: an insulating film; a thin filmthermistor portion made of the thermistor according to claim 1 on theinsulating film; and a pair of pattern electrodes formed at least on thetop or the bottom of the thin film thermistor portion.
 5. The film typethermistor sensor according to claim 4, wherein at least a portion of apair of the pattern electrodes that is bonded to the thin filmthermistor portion is made of Cr.
 6. A method for producing thethermistor according to claim 1, the method comprising a deposition stepof performing film deposition by reactive sputtering in anitrogen-containing atmosphere using a Ti—Cr—Al composite sputteringtarget.
 7. The method for producing the thermistor according to claim 6,wherein the sputtering gas pressure during the reactive sputtering isset to less than 0.67 Pa.
 8. The method for producing the thermistoraccording to claim 6, the method comprising a step of irradiating theformed film with nitrogen plasma after the deposition step.